Rice husk ash (RHA) and silica-filled nitrile rubber (NBR) composites were prepared using a laboratory-size two-roll mill. The mechanical properties and water absorption were studied before and after being exposed to gamma irradiation from 25 to 200 kGy. The tensile strength increased with RHA up to an optimum filler loading (20 phr) and (30 phr) for a silica-filled NBR composite. The tensile strength for the irradiated composite filled with 30 phr silica increases with an increase in irradiation doses up to 100 kGy. The presence of silica filler phase that has a higher electron density than the polymer matrix will likely result in an increase in cross-linking or scissioning and better dispersion in the matrix. Water absorption studies indicate that the irradiated NBR composite filled with silica has lower water absorption rather than the composite filled with RHA. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 301-311, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20225